Aftertreatment of rayon packages



, silk threads and the like.

Patented July 23, 1940 UNITED STATES? PATENT oFFicEj 2,208,965 AFTERTREATMENT F RAYON PACKAGES Jacob Dousnia, Ede, Gelderland, Netherlands, as-

signor to American Enka Corporation, Erika, N. 0., a corporation of Delaware No Drawing. Application March 23, 1939. Serial No. 263,808. In Germany April 12, 1938 6 Claims. (Cl. 18- -54=-) 13. form the spinning solution known as viscose.

The viscose, after a suitableripening period, is readyior spinning andis pumped through pipe lines to the spinning machineswhere it is extruded through minute openings of a spinneret into an acid bath where it is coagulated to form rayon thread. The freshly spun, wet thread, containing considerable impurities in the form of acids, salts and sulfur compounds, which must be removed, is wound on a bobbin or collected in the form of a cake in a centrifugal spinning pot.

Up to the present time the removal of sulfur and other impurities from the freshly spun rayon has involved a lengthy, tedious and rather expensive procedure. One method which has previously been pursued for washing and desulfurizing freshly spun packages of rayon is as follows: Rayon packages in the form of spools, cakes and the like were first washed repeatedly with cold water in a pressure or vacuum wash in order to remove the greater portion of impurities in the form of salts and acids which were present in the spinning solution, or which were acquired during passage of the thread through the coagulating bath. Thereupon the thread packages were subjected to washing with warm or hot water in order to remove all traces of salts and acids. In addition, the use of Water at higher temperatures had a tendency to more completely remove the carbon disulfide containedin the thread. It has always been highly desirable to remove the carbon disulfide as soon as possible because its presence retarded the subsequent desulphurizing and final washing operation. The yarn was then desulphurized by treating with alkaline desulphurizing agents such as solutions of sodium and ammonium sulfide, sodium sulfite, dilute sodium'hydroxide and the like. It then became necessary to expel the desulphurizing agents and was effected by washing the thread package in warm and cold water baths containing, if necessary, dilute acids to facilitate the removal of the alkaline desulphurizing' agents. As a further treatment, the thread package was also bleached preferably after desulphurizing.

Such a long drawn out procedure as that described above is highly objectionable for the reason that it requires in the neighborhood of from 12 to 20 separate operations, involving use of very large quantities of warm water and other treating fluids and necessitating the expenditure of considerable time and labor. Furthermore, freshly spun rayon threads are rather delicate, and extended manipulations give rise to strains that lower the quality of the finished product."

My invention is designed to overcome the ob- V jectionable characteristics of such a procedure, and one of its objects is the provisionof an improved process for washing and de'sulphurizi'ng rayon.

Another object of the invention is to effect a quick removal of carbon disulphide during washing and desulphurizing whereby substantial economy in operations is effected.

A further object of the invention is to accelerate the desulphurizing step and accentuate the action of the desulphurizing agent whereby the entire treating time is considerably shortened.

In carrying out my improved process freshly spun rayon packages are first washed for a short time with cold water. This prewashing serves to remove the greater portion of impurities in the form of salts and acids from the yarn, and is immediately followed by a treatment with a dilute alkaline desulphurizing agent at room temperature, for example a 0.15% sodium hydroxide solution, in order to dissolve the sulphur compounds present in the yarn and to neutralize the remaining traces of acids. The yarn package filled with the alkaline desulphurizing fluid is now subjected to the action of low pressure steam, for example at 0.3 atmosphere absolute pressure.

As stated before, the presence of carbon disulfide in the yarn package hinders the removal of the sulphur impurities, and consequently, to secure optimum desulphurizing conditions the carbon disulfide must be removed as quickly as possible from the yarn package. Carbon disulfide boils at 46 C., and the application of steam to the yarn package filled with the desulphurizing fluid causes heat to spread rapidly throughout the package, much more rapidly, in fact, than if it were attempted to raise the temperature of the package by heating the desulphurizing fluid prior to the treatment of the yarn therewith, for the reason that circulation of a fluid through the compact package takes place slowly. With the rise in temperature of the desiflphurizing fluid in the package as a result of the application of steam the carbon disulfide is quickly volatilized, and the alkaline desulphurizing solution, becoming heated as a result of the action of the steam, efiects a rapid and thorough removal of all of the sulphur impurities together with the carbon disulfide. The escaping carbon disulfide may be recovered, if desired, in any known manner. The yarn package is then Washed with hot and/or cold water 'to remove all of the residual impurities.

What is claimed is:

1. A method of treating freshly spun rayon comprising washing freshly spun rayon in package form with water, treating the same with an alkaline desulfurizing agent, disseminating the desulphurizing agent throughout said package bymeans of steam and again washing with water.

2. A method of treating freshly spun rayon comprising washing freshly spun rayon in package form with cold water until the greater portion of acids are removed, impregnating with an alkaline desulfurizing agent at room temperature, subjecting said impregnated package to the action of steam and finally removing the impurities by washing the package with water.

3. A method of treating freshly spun rayon which has been coagulated in an acid bath comprising washing freshly spun rayon in package form with cold water to remove the greater portion of salts and acids, treating with an aqueous alkaline desulfurizing agent at room temperature, subjecting said package to the action of steam and washing in successive baths of hot and cold water.

4. A method of treating freshly spun rayon which has been coagulated in an acid bath comprising washing freshly spun rayon in package form with cold water to remove the greater portion of salts and acids, treating with a solution containing 0.15% sodium hydroxide at room temperature, immediately subjecting said package to the action of low pressure steam at an absolute pressure of 0.3 atmosphere and washing in successive baths of hot and cold water.

5. A process for the after treatment of freshly spun packages of artificial silk threads which comprises washing the packages substantially free of acid and salts with cold water, then impregnating the same with an alkaline desulphurizing solution at room temperature whereby the remaining acids are neutralized, treating the impregnated packages with steam to expel the carbon disulphide and accelerate the desulphuriz ing action, and finally washing the packages with water.

6. A method of treating freshly spun viscose rayon which has been coagulated in an acid bath to form thread and the like and thereafter collected in package form which comprises washing the package of threads with cold water until the greater portion of acids and salts are removed therefrom, immediately treating the package with an alkaline desulphurizing agent to neutralize the remaining acids and dissolve the soluble sulphur compounds, heating and disseminating the desulphurizing agent throughout the package with steam to thereby accelerate the action thereof while volatilizing the carbon disulphide and effecting the simultaneous removal of the sulphur impurities together with the carbon disulphide and finally washing the package with water to remove the residual impurities.

JACOB DOUSMA. 

